1. Field of the Invention
The present invention relates to a semiconductor light emitting element.
2. Related Art
In general, a nitride III-V compound semiconductor such as gallium nitride (GaN) is a semiconductor having a wide-band gap. Making the most of its features, ultraviolet to blue and green light emitting diodes (LEDs) having a high luminance and blue-violet laser diodes (LDs) are under research and development.
For further raising the performance and efficiency of the semiconductor light emitting element, it is desired to lower the operation voltage of the semiconductor light emitting element. Typically, magnesium (Mg) is used as a p-type impurity for the nitride III-V compound semiconductor. Since the acceptor level of Mg is deep, however, Mg is hard to be activated as an acceptor. As a result, a voltage rise is brought about. It is important in lowering the operation voltage of the whole semiconductor light emitting element to lower the voltage in a p-type layer.
It is one technique to lower the voltage in a p-type contact layer as means for lowering the voltage in the p-type layer of the semiconductor light emitting element. The voltage acted on the contact layer depends upon contact resistance and series resistance. Above all, for lowering the contact resistance, it is desirable to increase the contact area for lowering the contact resistance.
It is proposed to provide an n-side layer with concavity and convexity in order to raise the light emitting efficiency if a light emitting diode (LED) (see, D. Morita, etc., “Watt-Class High-Output-Power 365 nm Ultraviolet Light-Emitting Diodes,” Japanese Journal of Applied Physics, September 2004, Vol. 43, No. 9A, pp. 5945-5950).
For raising the light emission efficiency, however, it is desirable to provide the p-type layer side located nearer the active layer with concavity and convexity. If it is attempted to provide the p-type layer with concavity and convexity by using the etching process technique, however, there is a fear that even the active layer might be damaged because the layer thickness is thin and a sophisticated etching process technique is needed. In other words, forming a concavo-convex layer by using etching is apt to damage the semiconductor crystal, resulting in degraded characteristics of the semiconductor light emitting element.